12 research outputs found
Density functional theory study of the NO<sub>2</sub>-sensing mechanism on a WO<sub>3</sub> (0 0 1) surface: the role of surface oxygen vacancies in the formation of NO and NO<sub>3</sub>
<p>The trapping and detection of nitrogen oxide with tungsten trioxide has become a popular research topic in recent years. Knowledge of the complete reaction mechanism for nitrogen oxide adsorption is necessary to improve detector performance. In this work, we used density functional theory (DFT) calculations to study the adsorption characteristics and electron transfer of nitrogen dioxide on an oxygen-deficient monoclinic WO<sub>3</sub> (0 0 1) surface. We observed different reactions of NO<sub>2</sub> on slabs with different O- and WO-terminated WO<sub>3</sub> (0 0 1) surfaces with oxygen vacancies. Our calculations show that the bridging oxygen atom on an oxygen defect on an O-terminated WO<sub>3</sub> (0 0 1) surface is the active site where an NO<sub>2</sub> molecule is oxidised into nitrate and is adsorbed onto the surface. On a WO-terminated (0 0 1) surface, one of the oxygen atoms from the NO<sub>2</sub> molecule fills the oxygen vacancy, and the resulting NO fragment is adsorbed onto a W atom. Both of these adsorption models can cause an increase in the electrical resistance of WO<sub>3</sub>. We also calculated the adsorption energies of NO<sub>2</sub> on slabs with different oxygen-deficient WO<sub>3</sub> surfaces.</p
Arginine-Assisted Hydrothermal Synthesis of Urchin-like Nb<sub>2</sub>O<sub>5</sub> Nanostructures Composed of Nanowires and Their Application in Cyclohexanone Ammoximation
Urchin-like Nb<sub>2</sub>O<sub>5</sub> nanostructures have been successfully synthesized by a novel and
simple l-arginine-assisted hydrothermal method. They are
characterized by X-ray diffraction (XRD), scanning electron microscopy
(SEM), high resolution transmission electron microscopy (HRTEM), nitrogen
adsorption–desorption isotherms, thermogravimetric and differential
thermal analysis (TG-DTA), and Fourier transform infrared spectroscopy
(FT-IR). The results show that the urchin-like nanostructures are
composed of nanowires with diameter less than 15 nm and possess a
high specific surface area of 249.9 m<sup>2</sup>·g<sup>–1</sup>. Urchin-like Nb<sub>2</sub>O<sub>5</sub> nanostructures have been
used for the first time as a novel catalyst instead of conventional
titanosilicate in the liquid-phase ammoximation of cyclohexanone.
The as-prepared urchin-like Nb<sub>2</sub>O<sub>5</sub> nanostructures
exhibit high catalytic activity in cyclohexanone ammoximation. Under
the optimal reaction conditions, the conversion of cyclohexanone and
selectivity of oxime are as high as 98.0% and 88.9%, respectively.
Finally, a possible formation mechanism of urchin-like Nb<sub>2</sub>O<sub>5</sub> nanostructures is proposed
Block Copolymer as a Surface Modifier to Monodisperse Patchy Silica Nanoparticles for Superhydrophobic Surfaces
Monodisperse
patchy silica nanoparticles (PSNPs) less than 100
nm are prepared based on the seed-regrowth method using a polyÂ(ethylene
oxide) (PEO)–polyÂ(propylene oxide) (PPO)–PEO-type block
copolymer as a surface modifier. Well-defined patches are controllably
synthesized through area-selective deposition of silica onto the surface
of seeds. After colloidal PSNPs are further modified with trimethylchlorosilane,
the advancing and receding contact angles of water for PSNPs are 168
± 2° and 167 ± 2°, respectively. The superhydrophobic
and transparent coatings on the various types of substrates are obtained
by a simple drop-casting procedure. Additionally, almost the same
superhydrophobicity can be achieved by using colloidal PSNPs via redispersing
the powder of superhydrophobic PSNPs in ethanol
Block Copolymer as a Surface Modifier to Monodisperse Patchy Silica Nanoparticles for Superhydrophobic Surfaces
Monodisperse
patchy silica nanoparticles (PSNPs) less than 100
nm are prepared based on the seed-regrowth method using a polyÂ(ethylene
oxide) (PEO)–polyÂ(propylene oxide) (PPO)–PEO-type block
copolymer as a surface modifier. Well-defined patches are controllably
synthesized through area-selective deposition of silica onto the surface
of seeds. After colloidal PSNPs are further modified with trimethylchlorosilane,
the advancing and receding contact angles of water for PSNPs are 168
± 2° and 167 ± 2°, respectively. The superhydrophobic
and transparent coatings on the various types of substrates are obtained
by a simple drop-casting procedure. Additionally, almost the same
superhydrophobicity can be achieved by using colloidal PSNPs via redispersing
the powder of superhydrophobic PSNPs in ethanol
Ionic Current Rectification in Organic Solutions with Quartz Nanopipettes
The
study of behaviors of ionic current rectification (ICR) in
organic solutions with quartz nanopipettes is reported. ICR can be
observed even in organic solutions using quartz pipettes with diameters
varied from several to dozens of nanometers, and the direction of
ICR is quite different from the ICR observed in aqueous phase. The
influences of pore size, electrolyte concentration, and surface charge
on the ICR have been investigated carefully. Water in organic solutions
affects the direction and extent of ICR significantly. Mechanisms
about the formation of an electrical double layer (EDL) on silica
in organic solutions with different amount of water have been proposed.
An improved method, which can be employed to detect trace water in
organic solutions, has been implemented based on Au ultramicroelectrodes
with cathodic differential pulse stripping voltammetry
Ionic Current Behaviors of Dual Nano- and Micropipettes
Ionic current rectification
(ICR) phenomena within dual glass pipettes
are investigated for the first time. We demonstrate that the ionic
flow presents different behaviors in dual nano- and micropipettes
when the two channels are filled with the same electrolyte KCl and
hung in air. Bare dual nanopipettes cannot rectify the ionic current
because of their geometric symmetry, but the ICR can be directly observed
based on bare dual micropipettes. The phenomena based on dual micropipettes
could be explained by the simulation of the Poisson-Nernst-Plank equation.
After modification with different approaches, the dual nanopipettes
have asymmetric charge patterns and show various ICR behaviors. They
have been successfully employed to fabricate various nanodevices,
such as ionic diodes and bipolar junction transistors. Due to the
simple and fast fabrication with high reproducibility, these dual
pipettes can provide a novel platform for controlling ionic flow in
nano- and microfluidics, fabrication of novel nanodevices, and detection
of biomolecules
Fabrication of Metal Nanoelectrodes by Interfacial Reactions
Despite
great improvements in the past decades, the controllable
fabrication of metal nanoelectrodes still remains very challenging.
In this work, a simple and general way to fabricate metal nanoelectrodes
(Ag, Au, and Pt) is developed. On the basis of interfacial reactions
at nano-liquid/liquid interfaces supported at nanopipettes, the nanoparticles
can be formed in situ and have been used to block the orifices of
pipettes to make nanoelectrodes. The effect of the driving force for
interfacial reaction at the liquid/liquid interface, the ratio of
redox species in organic and aqueous phases, and the surface charge
of the inner wall of a pipette have been studied. The fabricated nanoelectrodes
have been characterized by scanning electron microscopy (SEM) and
electrochemical techniques. A silver electrode with about 10 nm in
radius has been employed as the scanning electrochemical microscopy
(SECM) probe to explore the thickness of a water/nitrobenzene (W/NB)
interface, and this value is equal to 0.8 ± 0.1 nm (<i>n</i> = 5). This method of fabrication of nanoelectrodes can be extended
to other metal or semiconductor electrodes
Studies of Ionic Current Rectification Using Polyethyleneimines Coated Glass Nanopipettes
The modification of glass nanopipettes with polyethyleneimines
(PEIs) has been successfully achieved by a relatively simple method,
and the smallest tip opening is around 3 nm. Thus, in a much wider
range of glass pipettes with radii from several nanometers to a few
micrometers, the ion current rectification (ICR) phenomenon has been
observed. The influences of different KCl concentrations, pH values,
and tip radii on the ICR are investigated in detail. The sizes of
PEIs have been determined by dynamic light scattering, and the effect
of the sizes of PEIs for the modification, especially for a few nanometer-pipettes
in radii, is also discussed. These findings systemically confirm and
complement the theoretical model, and provide a platform
for possible selectively molecular detection and mimic biological
ion channels
PK/PD Disconnect Observed with a Reversible Endothelial Lipase Inhibitor
Screening of a small set of nonselective
lipase inhibitors against
endothelial lipase (EL) identified a potent and reversible inhibitor, <i>N</i>-(3-(3,4-dichlorophenyl)Âpropyl)-3-hydroxy-1-methyl-2-oxo-1,2-dihydropyridine-4-carboxamide
(<b>5</b>; EL IC<sub>50</sub> = 61 nM, EL<sub>HDL</sub> IC<sub>50</sub> = 454 nM). Deck mining identified a related hit, <i>N</i>-(3-(3,4-dichlorophenyl)Âpropyl)-4-hydroxy-1-methyl-5-oxo-2,5-dihydro-1<i>H</i>-pyrrole-3-carboxamide (<b>6a</b>; EL IC<sub>50</sub> = 41 nM, EL<sub>HDL</sub> IC<sub>50</sub> = 1760 nM). Both compounds
were selective against lipoprotein lipase (LPL) but nonselective versus
hepatic lipase (HL). Optimization of compound <b>6a</b> for
EL inhibition using HDL as substrate led to <i>N</i>-(4-(3,4<b>-</b>dichlorophenyl)Âbutan-2-yl)-1-ethyl-4-hydroxy-5-oxo-2,5-dihydro-1<i>H</i>-pyrrole-3-carboxamide (<b>7c</b>; EL IC<sub>50</sub> = 148 nM, EL<sub>HDL</sub> IC<sub>50</sub> = 218 nM) having improved
PK over compound <b>6a</b>, providing a tool molecule to test
for the ability to increase HDL-cholesterol (HDL-C) levels in vivo
using a reversible EL inhibitor. Compound <b>7c</b> did not
increase HDL-C in vivo despite achieving plasma exposures targeted
on the basis of enzyme activity and protein binding demonstrating
the need to develop more physiologically relevant in vitro assays
to guide compound progression for in vivo evaluation
Diphenylpyridylethanamine (DPPE) Derivatives as Cholesteryl Ester Transfer Protein (CETP) Inhibitors
A series of diphenylpyridylethanamine (DPPE) derivatives
was identified exhibiting potent CETP inhibition. Replacing the labile
ester functionality in the initial lead <b>7</b> generated a
series of amides and ureas. Further optimization of the DPPE series
for potency resulted in the discovery of cyclopentylurea <b>15d</b>, which demonstrated a reduction in cholesterol ester transfer activity
(48% of predose level) in hCETP/apoB-100 dual transgenic mice. The
PK profile of <b>15d</b> was suboptimal, and further optimization
of the N-terminus resulted in the discovery of amide <b>20</b> with an improved PK profile and robust efficacy in transgenic hCETP/apoB-100
mice and in hamsters. Compound <b>20</b> demonstrated no significant
changes in either mean arterial blood pressure or heart rate in telemeterized
rats despite sustained high exposures